REVIEW DRAFT—CISCO CONFIDENTIAL
14-14
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter14 Ethernet Operation
14.3.4 E-Series Q-Tagging (IEE E 802.1Q)
Figure14-12 Q-Tag Moving through VLAN
The ONS 15454 SDH uses the Q-tag attached by the external Ethernet devices th at support IEEE 802.1Q.
Packets enter the ONS network with an existing Q-tag; the ONS 15454 SDH uses this same Q-tag to
forward the packet within the ONS network and leaves the Q-tag attached when the packet leaves the
ONS network. The entry and egress ports on the ONS network must be set to Tagged for this process to
occur. Example 2 in Figure 14-12 illustrates the handling of packets that both enter and exit the ONS
network with a Q-tag.
For more information about setting ports to Tagged and Untag, refer to the Cisco ONS 15454 SDH
Procedure Guide.
Caution ONS 15454 SDHs propagate VLANs whenever a node appears on the n etwork view of another node,
regardless of whether the nodes are in the same SDH network or connect through DCC. For example, if
two ONS 15454 SDHs without DCC connectivity belong to the same logi n node group, VLANs
propagate between the two ONS 15454 SDHs. VLAN propagation happens even thoug h the
ONS 15454 SDHs do not belong to the same SDH ring.
Data Flow
No tag
Example 1.
The
ONS node
uses a
Q-tag internally to deliver
the frame to a specific VLAN.
The receiving
ONS node
removes the Q-tag
and forwards the frame
to the specific VLAN.
Example 2.
The
ONS node
receives
a frame with a Q-tag
and passes it on.
The receiving
ONS node
receives a frame with a
Q-tag and passes it on.
No tag
Q-tag Q-tag
Q-tag
Q-tag
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